This application is supplemental to Grant 2R01 NS 05572-15 (01-01-79 through 12-31-83) entitled "Cellular Aspects of Neurologic Disorders," for the performance of studies of Project 1 described in the above Grant ("The Study of Lymphoid and Neuronal Plasma Membranes and of their Interactions with the Golgi Apparatus or the Golgi Endoplasmic Reticulum System - GERL"), for which an updated electron microscope is essential. In addition, support is requested for the extension of the above project to include the study of cytologic and biochemical aspects of interactions between cloned murine neuroblastoma cells and cholera toxin. Specifically, we plan to investigate the endocytosis of cholera toxin and its exogenously introduced receptor (3HGM1). Furthermore, we will investigate the possible linkage of cholera toxin endocytosis to the regulation of the plasma membrane adenyl cyclase activity. Other studies will deal with the isolation and properties of the membrane fraction carrying the endocytosed toxin-receptor complex and to compare it with the plasma membrane fraction internalized during phagocytosis of polystyrene beads.